Apparatus and method for separating particles having different coefficients of friction

ABSTRACT

An apparatus and method for sorting or separating particles according to their different coefficients of friction, in which the particles move by gravity down a helical slide member until each particle establishes a stable trajectory radially equidistant from the helical axis of the slide member. The particles, after they have established their stable trajectories are then removed from the helical member by radially spaced discharge chutes.

United States Patent l Stafford i 1 Oct. 7, 1975 l l APPARATUS AND METHOD FOR SEPARATING PARTICLES HAVING DIFFERENT COEFFICIENTS OF FRICTION [76} Inventor: Richard D. Stafford, 710 S lst St.,

Nashville. Tenn 37210 {22] Filed: Dec. 26, 1973 [Zl] Appl No: 427.675

[52] US. Cl .i 209/II5; 209/112 [51] Int. Cl. B07B 13/10 [58] Field ofSearch 209/ll5, H6, H2

[56] References Cited UNITED STATES PATENTS 2,724,498 l l/l955 Beresford 209/1 12 FOREIGN PATENTS OR APPLICATIONS 450,853 4/l9l 3 France 209/] I6 Primary ExaminerAllen N. Knowles Attorney, Agent, or FirmHarrington A. Lackey ABSTRACT An apparatus and method for sorting or separating particles according to their different coefficients of friction, in which the particles move by gravity down a helical slide member until each particle establishes a stable trajectory radially equidistant from the helical axis of the slide member. The particles. after they have established their stable trajectories are then re moved from the helical member by radially spaced discharge chutes.

4 Claims, 3 Drawing Figures 28 M Mil/ U.S. Patent Oct. 7,1975

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APPARATUS AND METHOD FOR SEPARATING PARTICLES HAVING DIFFERENT COEFFICIENTS OF FRICTION BACKGROUND OF THE INVENTION This invention relates to an apparatus and method for sorting or separating particles, and more particularly to an apparatus and method for separating particles according to their coefficients of friction.

Various methods and apparatus for separation of particles are known. Many of these separation methods are based upon the differences in weight, density or size of the particles.

Although spiral or helical slides have been employed for separation of particles, the slides were screens or perforated sections adapted to separate the particles according to size.

Moreover, spiral guides and cyclones have been used for the separation of particles according to the centrifugal force exerted upon the particles of varied mass or shapes.

SUMMARY OF THE INVENTION It is an object of this invention to provide both an apparatus and method for separating particles according to their different coefficients of friction.

The particles are guided or permitted to move by gravity down a helical slide member. After the particles have descended down the helical slide member a sufficient distance, each moving particle stabilizes in a trajectory which is radially equidistant from the center of the helical slide member. The radial distance of the particle depends upon its coefficient of friction. Particles having a high coefficient of friction tend to establish tight circular trajectories close to the center of the helical slide member, while particles having low coefiicients of friction stabilize in trajectories radially farther away from the helical center. After the trajectories stabilize, then the particles are picked off by discharge chutes from their respective trajectories, to separate the particles in accordance with the values of their coefiicients of friction.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a top plan view of an apparatus made in accordance with this invention;

FIG. 2 is a side elevation of the apparatus disclosed in FIG. I, with parts broken away and partially in section; and

FIG. 3 is a section taken along the line 33 of FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings in more detail, the separating or sorting apparatus includes a helical slide member 12 having a solid upper surface 13 of uniform width.

Although the slide member 12 may be mounted in different ways, nevertheless it must be supported up right so that its helical axis is vertical. In the drawings, the inner edge 14 of slide member 12 abuts against, and is fixed to the outer surface of a cylindrical column 15 disposed concentrically within the center portion of the apparatus 10. The top portion of the column 15 may be cut off so that the inner edge 14 of the upper portion of the slide member 12 may communicate with the interior of the column 15. Lower down, as illustrated in FIG. 2, the wall of the column 15 may be cut out to form a slot or opening 16, also to permit free access between the inner edge 14 of the slide member 12 and the interior of the column 15.

The outer peripheral edge 18 of the slide member 12 is also helical and, as disclosed in the drawings, abuts the inner surface of the outer cylindrical wall 20. The slide member 12 may be fixed in position between the column 15 and the outer cylindrical wall 20 by structural members such as the triangular plates 22, the edges of which may be soldered or welded to the bottom surface 23 of the slide member 12 and the interior of the cylindrical outer wall 20.

An inlet chute 25 may be formed in the top portion of the apparatus 10 as a tangential extension of the upper end portion of the slide member 12, to receive particles to be separated.

The lower end of the column 15 terminates above the bottom of the outer wall 20 and communicates with a discharge chute 27 so that any particles passing from the slide member 12 over the inner edge 14 into the space within the hollow column 15 will be carried away from the apparatus I0 by the discharge chute 27. Such particles would be particles of very high coefficients of friction, such as rubber.

An inner discharge chute 28, an intermediate discharge chute 29 and an outer discharge chute 30 are arranged to tap into, or open through, the lower portion of the slide member 12 at different radial positions on the slide member 12. The relative elevations of the radial positions tapped by the respective discharge chutes 28, 29 and 30 is immaterial.

In the operation of the apparatus 10, such as in the sorting of automobile scrap material, particles, such as rubber 31, insulated copper wire 32, aluminum and copper 33, and zinc 34, of different coefficients of friction, are introduced upon the declining inlet chute 25 by any convenient conveyor means, such as a conveyor belt, not shown, so that the particles 31 34 are set in motion by gravity down the inlet chute 25. As the particles 31 34 move down and around the helical slide member 12, they will seek a stable trajectory based upon their respective coefficients of friction. Each particle 31 34 is subject basically to two forces, the force of gravity, that is the weight of the particle including the normal component of this force acting against the slide member 12 and the component moving the particle down the slide, and the frictional force acting between the top surface 13 of the slide member 12 and the engaging surface of the particle. The frictional force acts parallel and in opposition to the force of movement, which is the parallel component of the weight of the particle. Accordingly, each particle will move in a stable trajectory, after the initial oscillations of the particles have subsided.

Thus, for any given apparatus 10, the radial position of each particle 31 34, after the particle is stabilized, is solely a function of the coefficient of friction of that particular particle.

In FIG. 2, the stable trajectory of the particle 33 is illustrated by the radius r, and the fall per turn of the slide member 12 is illustrated by the distance h. The radius r is proportional to the fall per turn h. Accordingly, for any slide apparatus 10 in which the fall per turn h is fixed and constant, the stable trajectory of any particular particle will be fixed, and is a function only of its coefficient of friction. FIG. 3 also illustrates the particles 32, 33 and 34 in their respective stable trajectories.

Therefore, if it is desired to separate the particles into groups whose coefficients of friction correspond to the stable trajectories, such as those of the particles 32, 33 and 34 in FIG. 3, then the discharge chutes 28, 29 and 30 are correspondingly located to withdraw the particles at these particular radial positions. All particles having the same or similar coefficients of friction as the particle 32 will be discharged through the inner discharge chute 28. Particles having the same or similar coefficients of friction as the particle 33 will discharge over the chute 29, while the particles having the least coefficients of friction, corresponding to the particles 34, will exit over the outer discharge chute 30.

Particles of very high coefficients of friction, such as rubber 31, will tend to establish a trajectory within the inner edge 14 of the slide member 12, and will therefore fall over the edge 14 at some point in their downward movement, either into the top of the column 15, or through the slot 16 in the column 15, where they will be drawn off by the center chute 27.

It is also an important feature of the slide member 12 that any radial cross-section through the slide member 12 must be at an angle to the horizontal greater than but less than 90. A very satisfactory apparatus has been utilized in which the angle of the radial crosssection of the slide member 12 is approximately 45 to the horizontal, as disclosed in FIG. 2.

Generally speaking, when the radial cross-section of the slide member 13 is approximately 45 to the horizontal, the slide member 12 must have at least two or three turns to provide the particles sufficient time and distance to permit damping of the oscillations of the particles prior to stabilization of the particle trajectories before accurate separation can occur.

it is also important to the successful function of the apparatus 10, that all of the particles 31 34 must have shapes which will afford sliding frictional engagement between the particle and the top surface 13 of the slide member 12. if any of the particles are so shaped, or move with such velocity, that rolling friction is established between the particle and the sliding surface 13, then the frictional effect of the slide member 12 upon the particle is reduced so abruptly that the particle no longer moves in a stable trajectory. in fact, the rolling particles will be moved by centrifugal force to the outer edge 18 of the slide member 12 where they will ride against the inner surface of the outer wall 20, and ultimately be discharged through the outer discharge chute 30, regardless of their coefficients of sliding friction. Such rolling particles must be re-processed by, either introducing the particles into the inlet chute in such a manner that sliding friction is established, or reshaping the particles to eliminate the rolling friction contact.

It will of course be understood that after the particles are separated according to their coefficients of friction, that they will be fed by the respective discharge chutes 27 30 to appropriate deposit stations, receptacles or conveyors.

What is claimed is:

l. The method of separating non-spherical, metal scrap particles having different coefficients of friction comprising the steps of:

a. Selecting a plurality of said particles, at least some of which have different coefiicients of friction from the others, having shapes permitting said plurality of particles to have non-rolling, sliding movement down the continuous, uninterrupted surface of a helical slide member having a vertical axis,

b. feeding said plurality of particles downward substantially tangentially along the upper portion of said slide member surface causing said particles to have solely non-rolling, sliding movement down said surface of said helical slide member,

c. guiding said moving individual particles in sliding frictional engagement with the surface of said helical slide member for a predetermined number of a plurality of turns, causing said particles to follow trajectories dependent upon the individual coefficients of friction of said particles until each particle moves in a spiral stable trajectory radially equidistant from the center of said vertical axis,

. the position of each said particle in any radial, vertical plane of said helical path being disposed in a line at an angle to the horizontal of at least 0 and less than and e. removing groups of non-spherical, metal scrap particles of different coefficients of friction from correspondingly different stable trajectories on the slide member below said predetermined number of turns.

2. An apparatus for separating non-spherical, metal scrap particles having different coefficients of friction, comprising:

a. a helically-shaped slide member having a continu ous, uninterrupted, solid slide surface,

b. means supporting said slide member so that the helical axis of said slide member is vertical, and said slide member has an upper end portion and a lower end portion,

c. any radial cross-section of said slide member being at an angle to the horizontal greater than 0 and less than 90,

(:1. declining inlet chute means forming a substantially tangential extension of the upper end portion of said slide member for receiving a plurality of nonspherical metal scrap particles of different coefficients of friction and causing said particles to have solely non-rolling, sliding movement down said surface of said helical slide member,

e. said slide member having at least the critical number of helical turns necessary to cause each particle to move in non-rolling, sliding frictional engagement down said slide surface to establish its individual stable trajectory radially equidistant from said helical axis, and dependent upon the individual coefficient of friction of each particle,

f. a plurality of discharge outlets in the lower portion of said slide member, below the critical number of helical turns for a stable trajectory,

. each of said discharge outlets communicating with said slide member at a different radial distance from said helical axis corresponding to the radial trajectory of a particle to be separated.

3. The invention according to claim 2 in which said slide member has an outer helical edge terminating in an upright wall.

4. The invention according to claim 2 in which said angle to the horizontal is fixed.

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1. THE METHOD OF SEPARATING NON-SPHERICAL, METAL SCRAP PARTICLES HAVING DIFFERENT COEFFICIENTS OF FRICTION COMPRISING THE STEPS OF: A. SELECTING A PLURALITY OF SAID PARTICLES, AT LEAST SOME OF WHICH HAVE DIFFERENT COEFFICIENTS OF FRICTION FROM THE OTHERS, HAVING SHAPES PERMITTING SAID PLURALITY OF PARTICLES TO HAVE NON-ROLLING, SLIDING MOVEMENT DOWN THE CONTINUOUS, UNITERRUPTED SURFACE OF A HELICAL SLIDE MEMBER HAVING A VERTICAL AXIS, B. FEEDING SAID PLURALITY OF PARTICLES DOWNWARD SUBSTANTIALLY TANGENTIALLY ALONG THE UPPER PORTION OF SAID SLIDE MEMBER SURFACE CAUSING SAID PARTICLES TO HAVE SOLELY NON-ROLLING SLIDING MOVEMENT DOWN SAID SURFACE OF SAID HELICAL SLIDE MEMBER, C. GUIDING SAID MOVING INDIVIDUAL PARTICLES IN SLIDING FRICTIONAL ENGAGEMENT WITH THE SURFACE OF SAID HELICAL SLIDE MEMBER FOR A PREDETERMINED NUMBER OF A PLURALITY OF TURNS, CAUSING SAID PARTICLES TO FOLLOW TRAJECTORIES DEPENDENT UPON THE INDIVIDUAL COEFFICINETS OF FRICTION OF SAID PARTICLES UNTIL EACH PARTICLE MOVES IN A SPIRAL STABLE TRAJECTORY RADIALLY EQUIDISTANT FROM THE CENTER OF SAID VERTICAL AXIS, D. THE POSITION OF EACH SAID PARTICLE IN ANY RADIAL, VERTICAL PLANE OF SAID HELICAL PATH BEING DISPOSED IN A LINE AT AN ANGLE TO THE HORIZONTAL OF AT LEAST 0* AND LEASS THAN 90* AND E. REMOVING GROUPS OF NON-SPHERICAL, METAL SCRAP PARTICLES OF DIFFERENT COEFFICIENTS OF FRICTION FROM CORRESPONDINGLY DIFFERENT STABLE TRAJECTORIES ON THE SLIDE MEMBER BELOW SAID PREDETERMINED NUMBER OF TURNS.
 2. An apparatus for separating non-spherical, metal scrap particles having different coefficients of friction, comprising: a. a helically-shaped slide member having a continuous, uninterrupted, solid slide surface, b. means supporting said slide member so that the helical axis of said slide member is vertical, and said slide member has an upper end portion and a lower end portion, c. any radial cross-section of said slide member being at an angle to the horizontal greater than 0* and less than 90*, d. declining inlet chute means forming a substantially tangential extension of the upper end portion of said slide member for receiving a plurality of non-spherical metal scrap particles of different coefficients of friction and causing said particles to have solely non-rolling, sliding movement down said surface of said helical slide member, e. said slide member having at least the critical number of helical turns necessary to cause each particle to move in non-rolling, sliding frictional engagement down said slide surface to establish its individual stable trajectory radially equidistant from said helical axis, and dependent upon the individual coefficient of friction of each particle, f. a plurality of discharge outlets in the lower portion of said slide member, below the critical number of helical turns for a stable trajectory, g. each of said discharge outlets communicating with said slide member at a different radial distance from said helical axis corresponding to the radial trajectory of a particle to be separated.
 3. The invention according to claim 2 in which said slide member has an outer helical edge terminating in an upright wall.
 4. The invention according to claim 2 in which said angle to the horizontal is fixed. 